The present invention relates to a filter particularly for cleaning oil or fuel for an internal combustion engine. A typical filter of this type includes a filter housing, a replaceable filter cartridge, a supply conduit, a main drain conduit and a side drain conduit for draining the filter housing when removing the filter cartridge. A valve unit may be provided for such a filter with the valve maintained in a closed position by a lower front side of the filter cartridge when it is placed in the oil filter housing. A spring element is used to move the valve to an open position when the filter cartridge is removed. The valve comprises a sealing member, the first spring element biassing the sealing member in the opening direction, a seal seat, an activating member moveable relative to said sealing member in an axial direction, and a second spring element arranged between the sealing member and the activating member. The second spring member has a higher stiffness than the first spring element.
A filter of the kind mentioned is known from DE-40 22 723 A 1 wherein the disclosed filter is designed as a lube oil filter. With this known filter furthermore it is provided that the valve arranged in a side drain conduit is surrounded by a cylindrical valve housing, which preferably consists of an aluminum material, and is provided with a press fit area at the outer circumference thereof for pressing the valve housing into the side drain conduit. Furthermore it is proposed with this known filter that the activating member is guided at an inner area of the valve housing, and that the valve housing for limiting the axial movement of the activating member is comprised with a flanged edge at the upper end thereof. The spring constants of the two spring elements are harmonized with respect to each other such that firstly, the valve is held in closing position with the filter cartridge inserted, and that secondly, the valve is brought into the open position when taking the filter cartridge out of the filter housing, and that thirdly, with an erroneously lacking filter cartridge, the valve is brought into a closed position by oil pressure building up in the closed filter housing during operation of the associated internal combustion engine.
The known filter with the valve as described above comprises the required advantageous operation capacities, however, it is considered to be a disadvantage that for the manufacture of the valve a relatively high effort is required. This high effort particularly results from the fact that a dedicated valve housing is required which must manufactured for the valve, must be mounted with further parts of the valve and finally, must be finished, particularly comprised with a flanged edge.